1. Field of the Invention
This invention relates to a circumferential milling machine for milling along an arcuate portion of a cylindrical work piece having a cylindrical outer surface and, more specifically, to such a milling machine which is capable of milling a series of circumferentially space holes or slots, axially expanded holes or slots and/or tapered holes or slots in the arcuate portion of the cylindrical work piece.
2. Brief Description of the Prior Art
In the power industry, a number of steam power plants have been in existence for a number of years. These steam power plants include countless components, machines, equipment and systems which tend to degrade or malfunction with age and must be repaired or replaced with time. Further, in order to determine the status of such components, machines, equipment and systems with time, it is not uncommon for the operators of such power systems to rely on various testing and maintenance programs to detect and evaluate the condition and reliability of various components, machines, equipment and systems of the power plant.
One such area of the steam power plant includes the steam piping and distribution systems that are essential for the effective and safe operation of the of the plant. For example, many steam power plants utilize large cylindrical header pipes which include a plurality of smaller distribution pipes mounted on and extending from the headers. In such a header configuration, there would be a plurality of sets of pipes which would be generally mounted at one side of the header. Each set includes all the pipes thereof which are circumferentially separated and aligned with in a common arcuate sector of the cylindrical header. Each set of pipes is axially separated from adjacent sets of pipes. The terminal end of each pipe in each set extends perpendicularly from the outer cylindrical from the header. As each pipe of the set extends outwardly from the cylindrical header, it is bent or curved to be generally aligned with the other pipes of the set and with the pipes of the other sets axially separated therefrom so that all the pipes will be directed in the same direction generally away from the header.
The joining of each of the pipes in each set to the header is a critical and is subject to significant wear and deterioration with time. Accordingly, it has been found through elaborate nondestructive testing that weakened areas due to stress may develop in the regions of the header between the adjacent pipes of various sets of pipes. Such area affected by the stress tend to significantly weaken the header and have not been found to be correctable by simple welding or patching.
Accordingly, it has been found that the best and most reliable way to repair such a weakened header is to remove all of the pipes of a set, to completely remove all of the affected metal in the radial area and to replace it with weld material. However, the removal of the affected metal on the radial area has not been found to be a simple matter. In fact, it has been found to be extremely difficult. The headers are cylindrical in shape with thick walls that are typically made of high tensile steel. While there are numerous machining tools that are capable of removing such steel, there are significant problems with bringing and directing such tools to the cylindrical walls in a controllable manner in order to effectively and accurately remove the desired material. Additionally, any manner of removing the material must also be able to physically shape and form the hole that results in a proper condition for the receipt and retention of the new welding material.
When a portion of the header is found to have weakened stress areas that reduce its strength or reliability, the best way to reform the affected area first includes removing all of the pipes in the particular set of pipes in that area. If only one set of pipes are involved, the results would be a narrow arcuate area or portion the is physically located in the middle of the remaining array of sets of pipes. Clearly, accessibility to the affected area could be quite limited. Since it would be pointless and counter-productive to remove any pipes in unaffected areas simply to gain access to the affected areas, the problems of access and space limitations in a narrow arcuate area surrounded by a plurality of pipes is most significant.
Generally, if space were not an issue, there are any number machines or devices that could be used, at least to some extent, to remove material from at least a portion of a cylindrical surface. U.S. Pat. No. 4,459,883, discloses a portable machine tool for preparing pipe joints for welding but is installed within the interior of the large, hollow header. The tool components are small enough to be supported at the interior of the relatively thin walled header after they are passed through access holes. Such a system assumes that cutting or milling is only needed in the area of the pipes and that the header is of a type in which access openings are appropriate and, in fact, exist. U.S. Pat. No. 4,761,104 discloses a tube milling machine that appears to be mounted within a hole and able to mill a circular region around that hole but would not appear to be able to mill areas between adjacent hole or pipe ends such as could occur with the header problems discussed above. Similarly, U.S. Pat. No. 4,743,149 discloses a header tube tool that is specifically configure to prepare the cylindrical surface for the attachment of the ends of the pipes thereto. The tool is basically attached to the hole in the header and is configured to cut a circular area around the hole to generally provide a recess or socket into which the end of the pipe can be positioned for welding to the header.
There are various types of axial cutters for forming slots or key ways. U.S. Pat. No. 3,354,784 discloses a portable milling machine that can be mounted by a large bracketing framework to direct the cutting tool thereof to a limited axial region along the surface of the cylindrical surface of the work piece. U.S. Pat. No. 5,123,790 discloses an apparatus for milling grooves which is basically mounted on a work piece by a magnetic base. Such an apparatus would only be capable of effectively being mounted on a cylinder if it extends axially along the surface and it would then only be able to have the cutting tools to be advance axially along the surface of the cylinder to form a groove or key way that extends in the axial direction. Similar milling machines that move in the axial direction have been mounted to a cylinder by a self-centering device that is banded or strapped to the cylinder.
U.S. Pat. No. 5,161,291 discloses an adjustable machining apparatus for machining a cylindrical work piece to initially form the rotor teeth of a rotor core by the formation of a plurality of axial grooves therebetween. The milling tool is mounted on a device which is magnetically attached to the cylindrical outer surface of the rotor core. The milling tool can be primarily adjusted in three directionsxe2x80x94the first direction would be tangential to the outer surface, the second direction would be parallel to the axis of the core, and the third direction would be perpendicular to the tangential direction. The combined movement of in the first and second directions would generally allow the milling tool to be inserted into the cylindrical surface to form the groove cross-section and movement in the third axial direction would form the grooves to establish teeth therebetween. The tool can also be adjusted about an axis that is parallel with the axis of the rotor core to allow fine, controlled adjustment of the tool head within the grooves to be able to generally shape the cross-section of the grooves which can be continued along the lengths thereof by moving the entire tool relative to the mounting in the third axial direction.
Generally, while the devices and apparatus discussed above would be capable of milling some portions of a cylindrical surface, there is nothing taught therein that would suggest how one could conveniently remove the material in an axially narrow, relatively long arcuate portion of a cylindrical work piece without repeatedly mounting, removing, repositioning and remounting the device or apparatus at a number of circumferential locations about the cylindrical surface. Nevertheless, it would be possible to mill a relatively large arcuate section of the cylinder with a device having some of the features of that disclosed in U.S. Pat. No. 5,161,291. Any relatively portable milling device capable of moving the milling tool in the first, second and third direction could be mounted on the cylindrical surface to be supported generally tangentially on the surface of the cylindrical work piece. To generally mill a tangential cut in a radial portion the cylindrical work piece the milling tool must simply be moved back and forth in a tangential manner and moved axially inward after each pass in the same manner as one would saw a log. If one were to reposition the device at a different position around the cylindrical surface, a different tangential cut could be made to effectively enlarge the arcuate portion in which the material can be removed. However, such multiple transverse cuts would require repeated, inconvenient repositioning of the device and will not properly form the edges or sides of the resulting arcuate opening in the proper manner for welding.
It should be clear that none of the milling machines discussed above are configured to conveniently mill the arcuate portion of a header in a restrict area. U.S. Pat. No. 5,683,211 discloses a device and method of forming a groove in the outer cylindrical surface of a PVC conduit or duct and at least has a configuration the recognizes the basic problems that exists when working on a cylindrical surface. Since the conduit is only made of PVC, the system uses a hand held and controlled router rather than a milling machine. A cylindrical template is secured to the conduit in the area to be routed and an interior cylindrical surface is mounted at the supporting face of the router. Clearly such a system can not be effectively and reliably used to mill an arcuate portion of a cylindrical header made of steel.
It is an object of the present invention to provide a circumferential milling machine for milling along an arcuate portion of a cylindrical work piece having a cylindrical outer surface and a central axis.
It is another object to provide such a circumferential milling machine which includes mounting apparatus which capable of being mounted on the cylindrical outer surface at the arcuate portion and includes an arcuate supporting element which extends about the cylindrical work piece and has a center which is for being aligned with the central axis.
It is still another object to provide such a circumferential milling machine which is capable of being used to mill various holes and slots in the arcuate portion of the circumferential surface and to form cross-sections for the holes or slots that are particularly configured for filling with welding material.
It is a further object to provide such a circumferential milling machine which is capable of being used to mill the various holes and slots in the arcuate portion of the circumferential surface in a confined or restricted area.
It is yet another object to provide such a circumferential milling machine that can be easily installed at the desired location and can be selectively adjusted to conveniently and accurately mill throughout the arcuate portion.
These and other objects of the invention are provided in a preferred embodiment thereof including a circumferential milling machine for milling along an arcuate portion of a cylindrical work piece having a cylindrical outer surface and a central axis. The milling machine including a mounting configuration capable of being mounted on the cylindrical outer surface at the arcuate portion of the cylindrical work piece. The mounting configuration includes an arcuate supporting element which extends about the cylindrical work piece and has a center which is for being aligned with the central axis. A circumferential moving block is mounted on the arcuate supporting element for circumferential movement along the arcuate supporting element and about the center and the central axis in general alignment with the arcuate portion. The circumferential moving block is capable of being selectively disposed at a plurality of positions along the arcuate portion of the cylindrical outer surface. The circumferential moving block has a first end and a second end circumferentially displaced from said first end. A radial moving block is capable of being mounted at the first end of the circumferential moving block for radial movement with respect to the circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece. A milling device is rigidly mounted on the radial moving block and includes components for rotating a milling tool installed therein. The milling tool has an axis of rotation that is generally perpendicular to the cylindrical outer surface and extends through the central axis when the circumferential moving block is disposed at each of the plurality of positions along the arcuate portion of the cylindrical work piece.
In the circumferential milling machine, the radial moving block is alternatively capable of being mounted at the second end of the circumferential moving block for the radial movement with respect to the circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece.
The circumferential milling machine can further include a first axial moving block which is mounted for relative movement on the first end of the circumferential moving block in an axial direction which is parallel to the central axis when the circumferential moving block is disposed at each of the plurality of positions along the arcuate portion of the cylindrical work piece, wherein the radial moving block is mounted on the first axial moving block for the radial movement with respect to the first axial moving block and the circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece to cause the axis of rotation to continue to be generally perpendicular to the cylindrical outer surface and to extend through the central axis when the circumferential moving block is disposed at each of the plurality of positions along the arcuate portion of the cylindrical work piece and the axial moving block is selectively positioned along the axial direction relative to the circumferential moving block.
The radial moving block is alternatively capable of being mounted at the second end of the circumferential moving block for the radial movement with respect thereto. The circumferential milling machine can further include a second axial moving block which is like the first axial moving block and is mounted for relative movement on the second end of the circumferential moving block in the axial direction when the circumferential moving block is disposed at each of said plurality of positions along the arcuate portion of the cylindrical work piece. Accordingly, the radial moving block is mounted on the second axial moving block for the radial movement with respect to the second axial moving block and the circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece in the same manner as when the radial moving block is mounted at the first end of the circumferential moving block.
The circumferential milling machine can further include axial adjusting components operably mounted between the circumferential moving block and each of the first and the second axial moving blocks for selectively producing the relative movement of each of the first and the second axial moving blocks in the axial direction with respect to the circumferential moving block.
The circumferential milling machine can further include radial adjusting components operably mounted between each of the first and the second axial moving blocks and the radial moving block mounted thereon for selectively producing the radial movement of the radial moving block with respect to each of the first and the second axial moving blocks and the circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece.
In the circumferential milling machine, the mounting components can include a plurality of radially extending supports each having a first end secured to the cylindrical outer surface and a second end disposed outwardly of the cylindrical outer surface. The radially extending supports are circumferentially displaces along the arcuate portion of the cylindrical work piece. The arcuate supporting element includes a pair of circumferential ways which are axially displaced one from the other at equal distances along the lengths thereof. Each of the pair of circumferential ways are respectively mounted by adjustable mounting elements at each of the second ends of the plurality of the radially extending supports. Each of the adjustable mounting elements are selectively adjusted to cause the center of the arcuate supporting element and each of the circumferential ways thereof to be aligned with the central axis.
In the circumferential milling machine the circumferential moving block is mounted between the pair of circumferential ways. Each of the circumferential ways includes a fixed inner arcuate gear. The circumferential moving block includes a drive shaft which extends in the axial direction and has opposite end gears respectively aligned and engaged with the inner arcuate gears. The circumferential moving block includes circumferential adjusting components for selective rotation of the drive shaft and the opposite end gears thereof along the fixed inner arcuate gears to produce the circumferential movement of the circumferential moving block along the arcuate supporting element about the center and the central axis of the cylindrical work piece.
The circumferential adjusting components can include an adjusting shaft and attached worm mounted in the circumferential moving block adjacent and perpendicular to the drive shaft. The circumferential adjusting components include a worm gear rigidly mounted on the drive shaft and in meshing engagement with the worm and the adjusting shaft and attached worm are capable of being selectively rotated for the selective rotation of the drive shaft and the opposite end gears thereof.
In another embodiment, a circumferential milling machine is for milling along an arcuate portion of a cylindrical work piece having a cylindrical outer surface and a central axis. The circumferential milling machine includes mounting components capable of being mounted on the cylindrical outer surface at the arcuate portion of the cylindrical work piece. The mounting components include an arcuate supporting element which extends about the cylindrical work piece and has a center which is for being aligned with the central axis. The mounting components include a plurality of radially extending supports each having a first end secured to the cylindrical outer surface and a second end disposed outwardly of the cylindrical outer surface. The radially extending supports are circumferentially displaces along the arcuate portion of the cylindrical work piece. The arcuate supporting element includes a pair of circumferential ways which are axially displaced one from the other at equal distances along the lengths thereof. Each of the pair of circumferential ways are respectively mounted by adjustable mounting elements at each of the second ends of the plurality of the radially extending supports. Each of the adjustable mounting elements are selectively adjusted to cause the center of the arcuate supporting element and each of the circumferential ways thereof to be aligned with the central axis. A circumferential moving block is mounted on the arcuate supporting element between the pair of circumferential ways for circumferential movement along the arcuate supporting element and about the center and the central axis in general alignment with the arcuate portion. The circumferential moving block is capable of being selectively disposed at a plurality of positions along the arcuate portion of the cylindrical outer surface. Each of the circumferential ways includes a fixed inner arcuate gear. The circumferential moving block includes a drive shaft which extends in the axial direction and has opposite end gears respectively aligned and engaged with the inner arcuate gears. The circumferential moving block includes circumferential adjusting components for selective rotation of the drive shaft and the opposite end gears thereof along the fixed inner arcuate gears to produce the circumferential movement. The circumferential moving block has a first end and a second end circumferentially displaced from the first end. First and second axial moving blocks are respectively mounted for relative movement on the first end and the second end of the circumferential moving block in an axial direction which is parallel to the central axis when the circumferential moving block is disposed at each of the plurality of positions along the arcuate portion of the cylindrical work piece. A radial moving block is mounted on at least one of the first and the second axial moving blocks for radial movement with respect to the one of the first and the second axial moving blocks and the circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece. A milling device is rigidly mounted on the radial moving block and is for rotating a milling tool installed thereon. The milling tool has an axis of rotation that is generally perpendicular to the cylindrical outer surface and extends through the central axis when the circumferential moving block is disposed at each of the plurality of positions along the arcuate portion, of the cylindrical work piece and when one of the first and the second axial moving blocks is selectively positioned along the axial direction relative to the circumferential moving block.
The circumferential milling machine can further include axial adjusting components operably mounted between the circumferential moving block and one of the first and the second axial moving blocks for selective production of the relative movement of one of the first and the second axial moving blocks in the axial direction with respect to the circumferential moving block
The circumferential milling machine can further include radial adjusting components operably mounted between the one of the first and the second axial moving blocks and the radial moving block for selective production of the radial movement of the radial moving block with respect to the one of the first and the second axial moving blocks and circumferential moving block toward and away from the cylindrical outer surface and the central axis of the cylindrical work piece.
The circumferential adjusting components include an adjusting shaft and attached worm mounted in the circumferential moving block adjacent and perpendicular to the drive shaft. The circumferential adjusting components includes a worm gear rigidly mounted on the drive shaft and in meshing engagement with the worm and the adjusting shaft and attached worm are capable of being selectively rotated for the selectively rotation of the drive shaft.
One embodiment of the invention includes a method of milling of a type which is capable of providing at least one of a plurality of holes and slots along an arcuate portion of a cylindrical work piece having a cylindrical outer surface and a central axis. The method comprises the steps of:
mounting a milling device on the cylindrical work piece with a rotatable milling tool thereof in general alignment toward the arcuate portion and with an axis of rotation thereof that is generally perpendicular to the cylindrical outer surface and extends through the central axis;
selectively radially moving the milling device toward, away from and into the arcuate portion during rotation of the rotatable milling tool to be capable of producing milling of the arcuate portion of the cylindrical work piece; and
selectively circumferentially moving the milling device along a circumferential path aligned with the arcuate portion with a center of rotation along the circumferential path being maintained in alignment with the central axis and while maintaining the axis of rotation of the milling tool generally perpendicular to the cylindrical outer surface and through the central axis;
whereby a plurality of holes at circumferentially displaced locations along the arcuate portion are capable of being milled by the selectively circumferentially moving of the milling device including the rotatable milling tool which is a hole cutter sequentially to each of the displaced locations and then the selectively axially moving of the milling device during the rotation of the hole cutter toward and into the arcuate portion at each displaced location and whereby at least one slot which extends circumferentially in a arcuate sector of the arcuate portion is capable of being milled by the selectively radially moving of the milling device including the rotatable milling tool which is a side mill cutter into at least one location of the arcuate sector and then the selectively circumferentially moving of the milling device during the rotation of the side mill cutter as it is advanced throughout the arcuate sector.
The method of milling along an arcuate portion of a cylindrical work piece can further include the steps of installing the rotatable milling tool which is a tapered end mill cutter in the milling device and additionally milling by at least one of the selectively radially moving and the selectively circumferentially moving of the milling device during rotation of the tapered end mill cutter to produce a tapering of at least a portion of at least one of the hole and the slot.
The method of milling along an arcuate portion of a cylindrical work piece can further include the step of selectively axially moving the milling device at least in an axial direction which is parallel with the central axis while being aligned with the arcuate portion and while maintaining the axis of rotation of the milling tool generally perpendicular to the cylindrical outer surface and through the central axis, whereby at least one of the hole and the slot is capable of being milled by the selectively radially moving of the milling device including the side mill cutter into at least one of the hole and the slot and then the selectively axially moving of the milling device during the rotation of the side mill cutter to axially expand at least one of the hole and the slot in the axial direction.
The method of milling along an arcuate portion of a cylindrical work piece can further include the steps of installing the rotatable milling tool which is a tapered end mill cutter in the milling device and additionally milling by at least one of the selectively radially moving, the selectively circumferentially moving, and the selectively axially moving of the milling device during rotation of the tapered end mill cutter to produce a tapering of at least a portion of at least one of the hole and the slot which has been axially expanded.